The present invention relates to an optical element switching device for automatically switching parts necessary for various microscopic inquiries, and to an optical microscope loaded with the device.
When optical elements are switched in a conventional manner, the operator manually inserts or removes the optical elements required for various microscopic inquiries of the light field, dark field, differential interference and the like. For example, in a case of the reflection-type differential interference microscopic inquiry, a polarizer, a Nomarski prism, an analyzer and the like need to be inserted into an optical path, in addition to the generally employed light field microscopic inquiry.
The polarizer is an optical element inserted into an illuminated optical path to convert illumination light into linearly polarized light in a specific vibration direction. The Nomarski prism is an optical element for splitting the linearly polarized light which has passed through the polarizer into two linearly polarized light beams of mutually orthogonal vibration directions and overlapping again two reflected light beams from an observed specimen. One Nomarski prism common to the illumination light and the observation light is necessary in the case of the reflection observation, and a pair of Nomarski prisms for the illumination light and the observation light are necessary in the case of the transmission observation. The analyzer is an optical element for aligning the luminous fluxes which have passed through the Nomarski prism in the same vibration direction and interfering the luminous fluxes.
Further, a moving mechanism or a rotating mechanism is provided to vary the background color and adjust the contrast. The moving mechanism moves the Nomarski prism in a direction orthogonal with the optical axis. The rotating mechanism rotates the polarizer or the analyzer, in a plane orthogonal with the optical axis, relatively to a 1/4-wavelength plate arranged near the plane. Generally, the contrast is adjusted by manually operating the operation units of the moving mechanism and the rotating mechanism.
However, it is not preferable to use only one Nomarski prism for all of the objectives. If Nomarski prisms of different amounts of sharing (i.e. an amount of splitting two orthogonal linearly polarized light beams) are used in accordance with objectives used for observation, the contrast can be made more properly. For this reason, two or more Nomarski prisms are often switched for use, in accordance with the selected objectives.
In addition, the Nomarski prism is arrange, with its localization position set at the pupil position of the objective. At the localization position of the prism, two orthogonal linearly polarized light beams cross each other. For this reason, the position of the Nomarski prisms in the direction of the optical axis needs to be moved when objectives of different pupil positions are switched for use.
Generally, switching the Nomarski prisms in accordance with the switching of the objectives is operated manually by the user of the microscope.
For example, Utility Model Registration Publication No. 2556098 discloses a microscope of Nomarski interference contrast type as shown in FIGS. 23 and 24. This microscope comprises turrets 3 having a Nomarski prism 1 for an objective of a small magnifying power and a Nomarski prism 2 for an objective of a high magnifying power, a lifting mechanism for vertically moving the turrets 3 via gears 5 and 6 by turning a knob 4, and a switching mechanism for rotating the turret 3 and selecting the Nomarski prism in accordance with the magnifying power of the objective to be used.
According to this microscope, two Nomarski prisms 1 and 2 can be used separately by rotating the turret 3.
In addition, since the Nomarski prisms 1 and 2 are arranged so that lateral center lines of the Nomarski prisms 1 and 2 are arranged in the circumferential direction of the turret 3, the background color can be changed by rotating the turret 3 minutely. Also, the back-focus position (i.e. the pupil position) of each of the objectives and the localized position of the Nomarski prisms can be made coincide with one another by vertically moving the turret 3 by means of the lifting mechanism.
In the microscope, however, the interference colors are varied by only rotating the turret 3 minutely. In this case, the Nomarski prisms are moved while drawing arcs along the rotation of the turret 3. When the background color is varied, the optical axes of the Nomarski prisms are displaced in a normal direction to the vibration direction of the polarizer and the analyzer and the inherent optical performance cannot be achieved.
Moreover, when the Nomarski prism for the objective of a lower magnifying power is switched to that for the objective of a higher magnifying power by rotating the turret 3 together with switching of the objectives, and vice versa, adjusting again the background color to that observed before switching requires much labor.
In addition, since the amounts of sharing are different in accordance with the types of Nomarski prisms, the rate of variation of the background color to the rotation of the turret is varied in accordance with the types of the prisms, which gives a sense of incongruity to the observer.
Furthermore, although the background color to be observed by the observer, i.e. the retardation position is almost determined, the sensitivity in the drive of the prism cannot be varied at a position where the observation is required or a position where the observation is not required, and thereby it cannot be said that the microscope has definitely good operability.
For example, Jpn. Pat. Appln. KOKAI Publication No. 63-133115 discloses a microscope in which various microscopic inquiries can be selected by inserting various optical members into an optical path or removing them therefrom.
This microscope has a memory unit, an instructing unit and an inserting/removing control unit. The memory unit stores an inserted/removed state of the optical members corresponding to the respective microscopic inquiries. The instructing unit outputs instruction signals corresponding to the microscopic inquiries instructed by the operations of operation members. The inserting/removing control unit reads from the memory unit the inserted/removed states of the respective optical members corresponding to the microscopic inquiries instructed in response to the instruction signals and outputs signals to control the insertion of the optical members into an inserting/removing unit or removal of the optical members therefrom.
According to this microscope, labor required to manually insert the optical members into an optical path or remove them therefrom as seen in the prior art can be saved and a desired microscopic inquiry can be automatically selected by the only operations of the operation members.
In Jpn. Pat. Appln. KOKAI Publication No. 63-133115, however, a microcomputer instructs the insertion/removal control by reading the inserted/removed states of the various optical members at the time of differential interference observation, which are stored in the memory circuit, and consequently the optical members such as the Nomarski prisms, the polarizing plate and the 1/4-wavelength plate corresponding to the objectives in the optical path are inserted into the optical path.
At the time of the differential interference observation, the moving mechanism for moving the Nomarski prisms in a direction orthogonal with the optical axis, and the rotating mechanism for rotating the polarizer or the analyzer, in a plane orthogonal with the optical axis, relatively to the 1/4-wavelength plate arranged in the vicinity of the plane, as mentioned above, are required in order to adjust the contrast by changing the background color. But, the technique is not disclosed in this patent publication and it cannot be judged whether or not an invention described in the patent publication can be accomplished.
In addition, the system of rotating the polarizer or the analyzer in order to change the background color can be easily motorized comparatively, but has a drawback that its optical performance is inferior with respect to the points mentioned below, as compared with a system of moving the Nomarski prisms.
First, since the amount of variation in the phase difference can be kept in a range of -.lambda./2 to +.lambda./2, background colors in the sensitive color area cannot be obtained.
Secondly, since the light passing through the polarizer and the 1/4-wavelength plate is not a completely circular polarized light because of the influence of a half mirror for introducing the illumination light, the contrast is worsened.
Thirdly, since the 1/4-wavelength plate has an effect which any 1/4-wavelength plate should have in an only specific wavelength and the wavelength is shifted from the 1/4 wavelength in the other wavelength range, coloring occurs.
Finally, in accordance with a wedge angle which an element has, an image is displaced with the rotation of the element.